The present invention relates to a coordinate data input device of an electrostatic capacity type capable of detecting the position of a point on a screen touched mainly with a finger through the detection of a change in electrostatic capacity, and a method of fabricating such a coordinate data input device.
Recently, a coordinate data input device of an electrostatic capacity type generally referred to as tablet has been put to practical use. An operator is able to enter the x- and the y-coordinate of a point on the screen of the coordinate data input device by touching the point with a finger.
A conventional coordinate data input device has a printed circuit board, a sensing sheet using a rectangular dielectric film as a base film and placed on the printed wiring board, and a flexible wiring board electrically connecting the printed wiring board and the sensing sheet. The dielectric film of the sensing sheet is provided on its front surface with a plurality of parallel x-electrodes extended in parallel to the x-axis. Ends of the x-electrodes on the same side of the dielectric film serve as connecting ends, and a first connector is connected to the connecting ends of the x-electrodes. The dielectric film is provided on its back surface with a plurality of parallel y-electrodes extended in parallel to the y-axis. Ends of the y-electrodes on the same side of the dielectric film serve as connecting ends, and a second connector is connected to the connecting ends of the y-electrodes. The opposite ends of the flexible wiring board are connected to the connectors and the printed wiring boards to electrically connect the electrodes of the sensing sheet to drive circuits and control circuits formed on the printed wiring board.
When an operator's finger is put to an optional position on the sensing sheet, part of lines of electric force extending from the x-electrodes toward the y-electrodes is intercepted by the operator's finger to reduce lines of electric force reaching the y-electrodes, so that the electrostatic capacity changes, and the coordinates of the position touched with the operator's finger can be determined on the basis of an output current produced by the sensing sheet varying according to the variation of the electrostatic capacity.
As mentioned above, in the conventional coordinate data input device of an electrostatic capacity type, the x-electrodes and the y-electrodes formed on the sensing sheet are electrically connected through the connectors and the flexible wiring board to the printed wiring board. Therefore, the thickness of the coordinate data input device is dependent on the relatively great thickness of the connectors attached to the front and the back surface of the sensing sheet. Since the flexible wiring board is expanded toward one side of the sensing sheet and is extended to the printed wiring board, a relatively large space is required to layout the flexible wiring board, which increases the overall external dimensions of the coordinate data input device.